There is known a method of measuring an optical absorption characteristics of a sample in which the method comprises conducting a light to the sample so that the light is reflected on the sample by a total reflection, receiving the light that was reflected on the sample, and detecting the optical absorption characteristic of the sample on the basis of the received light in order to specify at least any one of a condition of a target substance in the sample, a kind of a target substance in the sample, a concentration of the target substance in the sample, and an amount of a target substance in the sample on the basis of the optical absorption characteristics of the sample.
In the above-mentioned conventional measuring method, an optical wave-guide is used for reflecting the light reflected on the sample by the total reflection.
The conventional optical wave-guide includes a trapezoid body or a rectangular parallelepiped body, so that the light is reflected by the total reflection several times in the optical wave-guide.
In the FIG. 12(a), there is shown such a conventional optical wave-guide that includes the trapezoid body. As shown in FIG. 12(a), the optical wave-guide has a pair of a light input surface 31 and a light output surface 32 that are opposite to each other, and a pair of an upper reflecting surface 33 and a bottom reflecting surface 34 that are opposite to each other. On the bottom reflecting surface 34, the sample 35 to be measured is disposed.
A laser light or a white light from a light source not shown in the drawing is entered into the optical wave-guide through the input surface 31, and the light continuously is reflected by the total reflection on the upper reflecting surface 33 and the bottom reflecting surface 34. The light is reflected by the total reflection on the sample disposed on the bottom reflecting surface 34 several times so that the optical absorptions are produced through every total reflection. The optical absorption characteristics depend on the kind of the target substance in the sample. Therefore, it is possible to specify the condition of the target substance, the kind of the target substance, the concentration of the target substance and the amount of the target substance in the sample by detecting the optical absorption characteristics of the sample from the light that was reflected on the sample by the total reflection in the optical wave-guide and then exited from the optical wave-guide (Referring the Japanese patent No. 2807777). For example the optical absorption characteristics may be any one of an amount of the optical absorption, an optical absorption intensity, and an optical absorption spectrum.
The measurement sensitivity of the above mentioned measuring method depends on the number of the reflecting times. More specifically, if the number of the reflecting times increases, the measurement sensitivity also increases. Conversely, if the number of the reflecting times decreases, the measurement sensitivity also decreases. Therefore, in order to increase the measurement sensitivity it is necessary to lengthen the optical wave-guide, or to thin the optical wave-guide, so that the number of the reflecting times is increased.
However, there is a technical limit in thinning the optical wave-guide.
Therefore, to increase the measurement sensitivity, it is actually necessary to lengthen the optical wave-guide. However, there is a problem that a device of large size for measuring the optical absorption characteristics should be used, if the optical wave-guide is lengthened.
If the optical wave-guide is lengthened, the number of reflecting times increases as shown in FIG. 12(b). However the area of the reflecting surface also enlarges, so that the amount of the sample to be required for measurement increases. Because it is difficult to extract the any kind of the samples that include a specimen that only trace amount thereof can be prepared or available, there is a serious problem that it becomes difficult to measure such a specimen if the increased amount thereof is required for measurement.
It is an object of the present invention to solve the above-mentioned problems and provide a method of measuring an optical absorption characteristics of a sample and a device for measuring an optical absorption characteristics of a sample that the amount of the sample to be measured can be minimized and the number of a total reflection can be suitably set by using an optical wave-guide having a minimized size.